| With the continuous development of RFID technology, it becomes more and more widely used in people’s daily life. In the near future, the technology of RFID will be gradually widespread. The performance of antenna which is the front-ending device of RFID system, will be greatly improved with the development of RFID, because antenna plays a key role in the whole system. The properties of antenna directly determine the efficiency of the reader.Microstrip antenna is widely applied to the RFID reader antenna due to all the following advantages, such as light weight, low cost, simple process of manufacturing, especially its good conformal shape, easy integration, low profile. The design of this article is based on microstrip antenna, contributing to two successful models of RFID reader antenna.At first, it summarizes the development history, current situation and future prospects of the technology of RFID and antenna in this article. Then it introduces the RFID system and the antenna, summarizes the key points of designing and application area of discrete frequency bands. Futhermore, it analyses the theoretical knowledge, including the analytical method, radiation mechanism, feed method and some methods to broaden the bandwidth of microstrip antennas.Finally, two models of RFID reader antenna working in UHF, are presented in this article. One is single frequency RFID reader antenna working in UHF. It is designed using rectangular microstrip antenna, by method of introducing an air cavity through dielectric layer, in order to increase impedance bandwidth and improve radiation characteristics. In addition, the air cavity regulates the resonant frequency by changing height of air cavity without varying the size of patch. The circular polarization of this antenna is realized by the use of perturbation. The return loss of this antenna is smaller than-lOdb (S11≤-10dB), and its impedance bandwidth is51MHz. Another antenna is dual-band RFID reader antenna. The structure of antenna is designed on two-tier microstrip antenna, between which is air cavity, leading to the increase of bandwidth and the regulation of resonant frequency. The circular polarization of this antenna is realized by the method of the feed to the center point of two adjacent sides of the lower radiation patch at the same time. The resonant frequency in VHF (low-band) is about900MHz, and the bandwidth is about60MHz. The resonant frequency in UF is about2.4GHz, and the bandwidth is250MHz. These two models of antenna apply well in UHF RFID reader, and the technology of air cavity will achieve better development. |
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